1. Technical Field
The present invention relates to a data communication system for transmitting a data packet from a transmitting side to a receiving side using a radio channel, a data transmitting device, a data transmitting method, a data receiving device, and a data receiving method. The present invention relates particularly to a data communication system and the like that can ensure a real-time property while overcoming a packet loss in a radio environment by transmitting a probe packet from a receiving side to a transmitting side at fixed intervals, and predicting a data packet lost on the receiving side on the basis of a state of reception of the probe packet and retransmitting the data packet to the receiving side on the transmitting side.
2. Background Art
The spread of broadband communication environments such as an ADSL (Asymmetric Digital Subscriber Line) and optical fiber and the spread of digitization of moving images in recent years have led to increased use of communication service requiring a real-time property, such as videoconferencing systems and real-time distribution of sound and moving images via the Internet. Further, in radio, which is in increasing use, real-time moving image communication service typified by wireless cameras has come into use with improvements in throughput. It is important to ensure a real-time property while overcoming a packet loss occurring on a network in such a communication.
Typical methods for QoS (Quality of Service) control in a conventional wired environment include FEC (Forward Error Correction) and ARQ (Automatic Repeat Request). FEC is a technique that adds redundancy to communication data. FEC has an excellent real-time property because a lost packet can be recovered without retransmission being performed within a correcting capability, but significantly lowers service quality when a packet loss exceeding the correcting capability occurs. On the other hand, ARQ is a technique that requests retransmission of a lost packet. Although ARQ enables recovery regardless of the number of lost packets, depending on the number of retransmissions, ARQ cannot ensure a real-time property, and similarly lowers quality.
Conventionally, as a method for compensating for disadvantages of both, there is an FEC/ARQ combination system described in Non-Patent Document 1 (Hiroyuki Tanaka and Yutaka Takahashi, “Modeling and Performance Analysis of Real-Time Hybrid FEC/ARQ”: IEICE Technical Report IN2004-22, pp. 13-18, June 2004) or the like.